One popular 'megaman zero x ciel fanfic' could be 'Zero's New Purpose'. It explores their relationship in a post - apocalyptic world. The story delves into how Zero protects Ciel and the challenges they face together.
Well, in 'zero x megaman fanfiction', the theme of loyalty is quite prevalent. They are loyal to each other and to their cause. Another common one is the exploration of power. How they use their powers and develop new ones. Also, the theme of sacrifice is often there. Sometimes one of them has to sacrifice something for the greater good of the world they are protecting.
Axl can be a great addition. He has his own unique abilities and a bit of a wilder personality compared to X and Zero, which can add some interesting dynamics. Also, Sigma is often included as a major antagonist. His complex motives and powerful presence make for great story material. Another good character is Alia. She can provide support to X and Zero from the base, and her intelligence can be used in various ways in the fanfiction, like helping to analyze enemy weaknesses.
The character development is often a great aspect. We get to see more of Zero and Ciel's personalities and how they grow together. For example, Ciel might become more confident with Zero's support.
One key element could be the character development. In Megaman Zero X, his journey and growth are important aspects. Leviathan, being another character, might bring in elements of conflict or alliance. Their interactions could lead to new plot twists. Also, the fanfiction might explore the world - building, like the post - apocalyptic setting which is characteristic of the Megaman series. It could describe how they navigate through the desolate landscapes and face various enemies.
One idea could be a crossover where Naruto characters gain the abilities of Megaman Zero. For example, Naruto could have Zero's saber and use it in his battles. Another idea is to set the story in a post - apocalyptic world like in Megaman Zero, but with Naruto characters trying to survive and restore peace. Maybe Sasuke could take on a role similar to Zero, being a lone warrior at first but then joining forces with others.
Zero himself could be the main character in a sense. Imagine he somehow gets transported to the Naruto universe. He'd be a fish out of water at first, but his combat skills and sense of justice would make him a force to be reckoned with. He could start to learn about chakra and ninjutsu, and use his knowledge from his own world to help or even lead the Naruto characters in battles against new threats.
One popular theme is the relationship between X and Zero. Their friendship and how they support each other in battles is often explored. Another theme could be their origin stories, like how they were created and what their initial purposes were. Also, alternate universes where they have different abilities or face different challenges are quite common in fanfiction.
In some fanfictions, there might be a story where Zero has to protect Megaman X at all costs. This could involve a situation where X loses his powers temporarily and Zero has to fight off hordes of enemies on his own while also trying to find a way to restore X's abilities. It could show the loyalty and friendship between them in a really intense way.
You can try fanfiction websites like FanFiction.net or Archive of Our Own (AO3). They have a large collection of fan - created stories, and you can easily search for zero x megaman x fanfiction using the search bar on those sites.